The present invention relates to the power supply apparatus of the electric spark (discharge) machine. More particularly, the present invention relates to an improved control circuit for a switching circuit of the power supply apparatus, which is applied for any type of intermittent energy-generating block of the electric spark machine.
Most of the prior power supply for the electric spark machine were systems transforming the commercial AC power supply by a low frequency transformer, rectifying through the rectifier, restricting the output current by a resistor and supplying to the electrode gap. Recently, the technology for the power supply that it could provide a requested voltage and current by the pulse width control using switching circuit through direct rectification of the commercial AC source and converting it to high frequency pulse was developed. By this technology, the whole of the power supply apparatus becomes smaller and lighter toward the output capacity because it can be applied in the lightweight and the high efficiency high frequency transformer.
Also, technology was developed that reduces the allowable current value of the restricting resistor or it has no resistor, by restricting the output current.
There are Japanese Non-examined Patent Publication No.54-2595, No.57-138526 and No.5-208316 and Japanese Examined Patent Publication No.57-4452 and so on as the typical examples of such prior art. The technology of an intermittent energy-generating block itself for the electric discharge includes a switching element, and applied the restriction of electric discharge current is described in Japanese Examined Patent Publication No.57-4452. However, the relationship corresponding to the output current and the output voltage between the load-less voltage and the electric discharge start voltage is not controlled intentionally in this prior art.
In Japanese Non-examined Patent Publication No.54-2595 and No.57-138526, the intermittent energy-generating block itself for the electric discharge includes a switching element, and the restriction of the electric discharge current is carried out.
In Japanese Non-examined Patent Publication No.5-208316, the switching element is used for two steps, in the first step, it is used for the DC supply, and in the second step, it is used as the intermittent energy-generating block for the electric discharge and the discharge current is restricted. Also a capacitor is used as the intermittent energy-generating block for the electric discharge, and the power is supplied at its previous step by switching element in Japanese Non-examined Patent Publication No.S54-164086.
Moreover, there is the following disadvantage in the method by setting only a current restriction on the usual fixed voltage switching power supply for the electric discharge processing. A certain higher load-less voltage is necessary so that it causes easily a dielectric destruction at the electrode gap, i.e. the electric discharge starts, and it provides to maintain the stable servo control which is so-called stable electric discharge. Therefore, when a usual switching power supply is applied, it is required to provide this high load-less voltage. This had to be designed that all of the power supply elements have larger maximum consumption electric power capability. It obstructs to miniaturize and to lighten the power supply apparatus including the transformer.
There are Japanese Non-examined Patent Publication No.54-62595, No.56-163830, and No.5-285730 and Japanese Examined Patent Publication No.57-4452, and so on as a prior art, which solves these problems. However, all of these prior arts are consist of the combination of low voltage and high voltage power supply block, and then, it obstructs to miniaturize and to lighten the power supply because it is required two different type of the power supply circuits.
Though considerable miniaturization or weight decreasing or higher efficiency of the power supply for the electric spark machine have been developed by the above prior arts, it is important to provide further miniature and light weight power supply. Even in the country or the area where a higher commercial electric voltage is available higher for obtaining a load-less high voltage easily, it is important to control the discharge current and voltage, and to save the electric power consumption.
The object of the present invention is to provide the smaller size, the lighter weight and the more efficient power supply for the electric spark machine. Further object is to find a control circuit which has the characteristics to generate the high voltage so that it controls easily the steady electric discharge by only one switching power supply based on low voltage and large current.
The object of the present invention is to provide a smaller size and a lighter weight power supply apparatus for the electric spark machine than that of the prior arts. More particularly, the object is to provide a control circuit for a fly-back switching power supply, which has the characteristics to generate the high voltage to start the electric discharge easily by using only one switching power supply for low voltage and large current capacity. Another object is to provide an efficient power supply for the electric spark machine.
According to one of the preferable embodiment of the present invention, above objects are achieved by a control circuit having the feature which comprises controlling an output voltage for an intermittent energy-generation block so that the output voltage varies as the relation of a negative linear proportion against an output current in the range of the output voltage between the load-less voltage and the electric discharge start voltage plus minus 25V.
This control circuit has a feedback function which maintains the difference to be a constant by comparing the voltage of the summation of the output voltage and the voltage converted from the output current value with the predetermined standard voltage.
According to another preferable embodiment of the present invention, above objects are also achieved by a control circuit having the feature which comprises controlling an output voltage for an intermittent energy-generation block so that the output voltage varies as the relation of an inverse proportion against an output current in the range of the output voltage between the load-less voltage and the electric discharge start voltage plus minus 25V. This control circuit has a function that maintains the difference which obtained by comparing the voltage of the product (multiplication) of the output voltage and the voltage converted from the output current value with the predetermined standard voltage to a certain value.
These control circuits result in a reduction of the overall weight and size of the power supply.
A power supply for the electric spark machine of the 250VA output capacity is provided with about 1000 cubic cm in volume and about 1 Kg in weight by the present invention. By the prior technology of the combination with the low frequency transformer and the restriction resistor, it is about 4000 cubic cm in volume and about 10 Kg in weight. By the prior technology of the combination with two switching power supplies of high voltage and low voltage is about 2000 cubic cm in volume and about 2 Kg in weight.
Further, although it requires that each circuit component have 900VA capability by the combination of prior transformer and the restricting resistor in the case of manufacturing a power supply which has the load-less voltage of 180V and the output current capacity of 5A, in the case of the negative proportional relation of the present invention, since the maximum consumption of the power is about 311VA, all circuit components may be allowed to have only 311VA capability, also in the case of the inverse proportional relations of the present invention, since the maximum output voltage which corresponds the maximum output current 5A is about 50V, all circuit components may be allowed to have only 250VA capability, this results a higher efficient power supply. Many other features, advantages and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying sheet of drawings.
It is well known that a certain high voltage is required for the power supply to start the electric discharge on the gap between the work and the electrode. Also the power supply requires large current capability to maintain the intermittent electric discharge. Thus, each component of the circuit requires both high voltage and large current capability. It results large size and heavy weight power supply apparatus.
The advantage of the power supply which supplies relatively high voltage in the small current region and relatively low voltage in the large current region is understood. Thus, a control circuit which controls the switching circuit so that the output voltage for the intermittent energy-generation block varies as a negative linear proportion or an inverse proportion against the output current is provided for this purpose.
The argument of the control circuit for a negative linear proportion as follows:
obtaining the summation of the output voltage and the voltage converted from the detected output current, which is supplied to the intermittent energy-generating block;
comparing the summation voltage and the predetermined voltage by a comparing circuit; and
operating feedback the difference voltage of the summation voltage and the predetermined voltage to the fly-back switching circuit so that the difference voltage maintains a constant.
Resulting a negative proportion relation is understood by following equations.
Sxe2x88x92D=Constant i.e. S=D+Constant
S=Y+X i.e. Y=xe2x88x92X+D+Constant
Where, S is the summation of the voltage; D is the predetermined voltage; Y is the output voltage; and X is the voltage converted from the output current.
Since D is also a constant value, Y (i.e. output voltage) varies as a negative linear proportion by X (i.e. the voltage converted from the output current).
Also the argument of the control circuit for an inverse proportion as follows:
obtaining the product (multiplication) of the output voltage and the voltage converted from the detected output current, which is supplied to the intermittent energy-generating block;
comparing the product (multiplication) voltage and the predetermined voltage set in advance by a comparing circuit; and
operating feedback the difference voltage of the product (multiplication) voltage and the predetermined voltage to the fly-back switching circuit so that the difference voltage maintains a constant.
Resulting an inverse proportion relation is understood by following equations.
Pxe2x88x92D=Constant i.e. P=D+Constant
P=Yxc3x97X i.e. Y=(D+Constant)/X
Where, P is the product (multiplication) of the voltage; D is the predetermined voltage; Y is the output voltage; and X is the voltage converted from the output current.
Since D is also a constant value, Y (i.e. output voltage) varies as an inverse proportion by X (i.e. the voltage converted from the output current).
Also, the combined control circuit with above summation and above product may apply for this purpose if it is not inconvenient for a relative complex circuit.
The term xe2x80x9cintermittent energy-generating block for the electric dischargexe2x80x9d used herein, it means the element which has the function that it generates and supplies an electric energy to the electrode gap intermittently, for example, such as a capacitor, a capacitor and a coil, and a switching circuit combined an oscillation circuit with a transistor, a FET, a thyristor and so on.
Also, the term xe2x80x9coutput voltagexe2x80x9d used herein, it means the voltage supplied to the intermittent energy-generating block for the electric discharge. As for the term xe2x80x9coutput currentxe2x80x9d, it means the electric current between the high frequency rectification block and the intermittent energy-generating block for the electric discharge.
If the impedance value of the intermittent energy-generating block for the electric discharge is not so large, the output voltage and the output current are nearly equal to the so-called electrode gap voltage and electric discharge current respectively.
Further, the term xe2x80x9coutput voltagexe2x80x9d and xe2x80x9coutput currentxe2x80x9d used herein, it means so-called average voltage and average current respectively.
Generally, though so-called xe2x80x9csteady electric discharge voltage rangexe2x80x9d in the electric discharge processing is varied by the kind of the processing liquid or the electrode material, it is about 40V plus-minus 15V. Therefore, it is prefer to use a high frequency transformer which winding ratio provides the maximum efficiency in near about 40V as the output transformer.
From the conception of the usual transformer for example, although it is thought a difficulty that it gets the output voltage of 180V by using the high frequency transformer of the winding ratio that it gets the output voltage of 40V from the input voltage of 140V, however, it can be done easily to generate a higher output voltage than the input voltage to use a fly-back switching circuit without regard to the winding ratio of the transformer. This technology doesn""t cause a wrong influence on the process of electric spark machine processing even in the country or the area that the input voltage is 180V or more.
The fly-back switching circuit is based on the polarity reversal of the high frequency transformer and the output voltage generates at off time of the switching transistor, it generates a wide range of optional high voltage by adjusting the ratio of the on/off time of the switching.
The technology of restricting an electric discharge current is a well-known technology. This prior art also can be applied for the present invention, as the restricted current value is near value which is less than allowable value for the high frequency transformer.
The relationship between the output voltage and the output current in the range from the load-less voltage to near the electric discharge start voltage may be a negative linear proportion or an inversely proportion, but it may not be completely strict.
FIG. 1 shows the relationship between the output voltage and output current, as the vertical axis is the output voltage and the horizontal axis is the output current, including the difference from the prior art.
Solid straight-line Vo-A-M shows that the switching circuit is controlled as that the output voltage changes as a negative linear proportion against the output current in the present invention. It may allow to be some upper vending curve relation (Dotted line Vo-Axe2x80x2-M), however, it is not desirable because it comes off the relation which provides originally a high voltage at low current and a low voltage at large current when it is extreme offlying.
On the other hand, where the switching circuit is controlled as that the output voltage changes as an inversely proportion, (Solid line Vo-B-M) against the output current in the present invention, it allows to be applied without trouble because the required function is provided to generate substantially higher voltage even if the relation is extreme close to the hyperbola. (Dotted line Vo-Bxe2x80x2-M)
The range of the output voltage that the output voltage varies a negative linear proportion or inverse proportion against the output current may be between load-less (open) voltage and near the electric discharge starting voltage. However, if the bottom limit voltage of the output voltage is too high, it is not preferable because it requires higher capacity of elements for the power supply apparatus at large current.
Contrary, if the bottom limit voltage of the output voltage is too low, it is not desirable because the current value at the steady electric discharge stage falls down under desired value.
Finally, the preferable controlling range of the output voltage, which is expected the result of miniaturization or the lightening weight, is between the load-less voltage and the voltage of the electric discharge start voltage plus-minus 25V. (The part C of the FIG. 1)
Further, the alternate long and short line F of the FIG. 1 shows the relationship between the output voltage and the output current where the switching power supply is combined with a switching power supply for low voltage-large current and high voltage-small current as the prior art. The current restriction resistor is required to obtain the relation of a negative linear proportion between the electrode gap voltage and electric discharge current if it is used the prior low frequency transformer.
When the electrode gap resistance is short circuit or becomes small value like short circuit, large current flows unless the current restriction is carried out, and to cope with it, the larger power supply apparatus is required because the transformer and the restriction resistor of the large capacity should be necessary in this prior art.
The principle to control the switching circuit according to the present invention is described as follows.
First, the load-less voltage is set to the requested voltage. While decreasing the distance between the gap, once the electric discharge starts, then the current starts to flow and the above mentioned voltage of summation (or product) exceeds the predetermined standard voltage, then the equivalent quantity of the voltage converted from the current makes feedback as to short T-on for the switching so that the output voltage start to decrease. This trend maintains the relation of the negative proportion (or inverse proportion) that the output voltage is decreasing against the current is increasing.
It is preferable to use an OP amplifier for the addition operation circuit to obtain the summation of the voltage and to use an OP amplifier for multiplication operation to obtain the product of the voltage respectively. However, other circuit elements may be applied, if it has similar function.
The current restriction circuit is set separately. This circuit may be an OP amplifier, a three-terminal regulator, and like this. The setting is carried out so that the current restriction starts. The output voltage that the current restriction is started, can be set optionally by changing resistor value for converting the detected current to the voltage, and so on.
The element of the intermittent energy-generating block for the electric discharge in the present invention, may be applied any of a capacitor or the combination with a capacitor and an inductance, or the combination with the oscillation circuit and a transistor, a thyristor, a FET (Field Effect Transistor), and so on.